This invention relates generally to the cleaning of sludge from storage tanks, and more particularly to an apparatus for circulating crude oil through a crude oil storage tank to facilitate resuspension and removal of the sludge into the crude oil.
The manufacture of petroleum-based products begins with the pumping of crude oil from one or more wells. The crude oil is directed from the wells into one or more storage tanks comprising a tank battery. The oil is then transported most commonly by pipeline to storage tanks at oil refineries prior to processing.
As will be apparent, when contained in a storage tank crude oil is in a quiescent state. This allows any solid components and the heavier liquid components comprising the crude oil to settle to the bottom of the storage tank in the form of sludge. Sludge build up in the bottom of a crude oil storage tank is undesirable for a number of reasons, the most apparent of which is reduction of the storage capacity of the tank. A number of systems have heretofore been developed to reduce sludge build up in crude oil storage tanks. Several of these techniques involve the circulation of crude oil into the bottom of the tank in an attempt to resuspend the sludge in the crude oil.
One problem that has characterized prior tank cleaning apparatus and sludge removal systems is a significant pressure drop and flow turbulence created by the perforations and/or around the ninety degree bends that exist in present jetting apparatus. Reduction in pressure and flow turbulence cause a reduction in the flow rate, or velocity, of the crude oil that is being used to resuspend the sludge, ultimately leading to a significant reduction in system efficiency.
The present invention comprises a tank cleaning apparatus which overcomes the foregoing and other problems that have long since characterized the prior art. In accordance with the broader aspects of the invention, crude oil is pumped through a long, straight passageway and is discharged therefrom through a nozzle into the bottom of a crude oil storage tank. By this means the significant pressure drop which has characterized the operation of prior sludge removal systems is eliminated. For example, the present invention has less than 50% of the pressure drop of the prior systems known to the inventor.
Also, the elimination of the sharp bends through the apparatus greatly reduces turbulence in the flow. This in turn allows for a more focused and straighter discharge from the nozzle, i.e., a laminar flow stream, which substantially increase the efficiency of the system.
Another important aspect of the invention is the location of all moving components externally of the tank, excepting the outlet end of the straight pipe and the interior side of the gimbal. The apparatus may be permanently left on the tank without concern for the apparatus becoming inoperable due to sludge buildup within the apparatus, thus providing a significant advantage over the prior sludge removal systems.
The present invention may employ reciprocating movement of the gimbal and straight pipe in one plane in order to substantially increase system efficiency.
It is an advantage of the present invention to provide a tank cleaning apparatus which does not require the tank to be removed from service for cleaning.
It is an advantage of the present invention to eliminate the need for manual cleaning or opening the tank to the outside environment during cleaning.
It is an advantage of the present invention to eliminate the cost and need for manual cleaning prior to tank inspection and servicing.
It is an advantage of the present invention to allow tank operators to decontaminate their tanks for service changes without decommissioning the tank.
It is an advantage of the present invention to operate on the tank as a closed system, eliminating the need to vent the tank to atmosphere prior to, during, or after cleaning.
It is an advantage of the present invention to allow either use of the oil from the tank itself or the use of a fluid from an outside supply source, such as a source of cutter stock, to clean the tank.
It is an advantage of the present invention to provide a tank cleaning apparatus which will interface between two dissimilar environments, i.e., the exterior, natural atmosphere outside of the tank and the interior contents of the tank, thereby eliminating the need to decommission the tank before, during, or after cleaning by permanently installing the tank cleaning apparatus on the tank.